#1 will eventually be addressed with a multi-thread patch to the various RAID drivers including RAID5
what is the differences between the multi-thread patch and the CONFIG_MULTICORE_RAID456?
my understanding is CONFIG_MULTICORE_RAID456
enum {
STRIPE_OP_BIOFILL,
STRIPE_OP_COMPUTE_BLK,
STRIPE_OP_PREXOR,
STRIPE_OP_BIODRAIN,
STRIPE_OP_RECONSTRUCT,
STRIPE_OP_CHECK,
}; this operations in a stripe can be schedule to other CPU to run,
while multi-thread patch mainly modify lock contention of thread, this understanding is correct?
------------------------------------------------------------------
发件人：lilofile <lilofile@xxxxxxxxxx>
发送时间：2013年11月28日(星期四) 19:54
收件人：stan <stan@xxxxxxxxxxxxxxxxx>; Linux RAID <linux-raid@xxxxxxxxxxxxxxx>
主 题：答复：答复：md raid5 performace 6x SSD RAID5
I have change stripe cache size from 4096 stripe cache to 8192, the test result show the performance improve <5%, maybe The effect is not very obvious。
------------------------------------------------------------------
发件人：Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx>
发送时间：2013年11月28日(星期四) 12:41
收件人：lilofile <lilofile@xxxxxxxxxx>; Linux RAID <linux-raid@xxxxxxxxxxxxxxx>
主 题：Re: 答复：md raid5 performace 6x SSD RAID5
On 11/27/2013 7:51 AM, lilofile wrote:
> additional: CPU: Intel(R) Xeon(R) CPU X5650 @ 2.67GHz
> memory:32GB
...
> when I create raid5 which use six SSD(sTEC s840),
> when the stripe_cache_size is set 4096.
> root@host1:/sys/block/md126/md# cat /proc/mdstat
> Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
> md126 : active raid5 sdg[6] sdf[4] sde[3] sdd[2] sdc[1] sdb[0]
> 3906404480 blocks super 1.2 level 5, 128k chunk, algorithm 2 [6/6] [UUUUUU]
>
> the single ssd read/write performance :
>
> root@host1:~# dd if=/dev/sdb of=/dev/zero count=100000 bs=1M
> ^C76120+0 records in
> 76119+0 records out
> 79816556544 bytes (80 GB) copied, 208.278 s, 383 MB/s
>
> root@host1:~# dd of=/dev/sdb if=/dev/zero count=100000 bs=1M
> 100000+0 records in
> 100000+0 records out
> 104857600000 bytes (105 GB) copied, 232.943 s, 450 MB/s
>
> the raid read and write performance is approx 1.8GB/s read and 1.1GB/s write performance
> root@sc0:/sys/block/md126/md# dd if=/dev/zero of=/dev/md126 count=100000 bs=1M
> 100000+0 records in
> 100000+0 records out
> 104857600000 bytes (105 GB) copied, 94.2039 s, 1.1 GB/s
>
>
> root@sc0:/sys/block/md126/md# dd of=/dev/zero if=/dev/md126 count=100000 bs=1M
> 100000+0 records in
> 100000+0 records out
> 104857600000 bytes (105 GB) copied, 59.5551 s, 1.8 GB/s
>
> why the performance is so bad? especially the write performace.
There are 3 things that could be, or are, limiting performance here.
1. The RAID5 write thread peaks one CPU core as it is single threaded
2. A 4KB stripe cache is too small for 6 SSDs, try 8KB
3. dd issues IOs serially and will thus never saturate the hardware
#1 will eventually be addressed with a multi-thread patch to the various
RAID drivers including RAID5. There is no workaround at this time.
To address #3 use FIO or a similar testing tool that can issue IOs in
parallel. With SSD based storage you will never reach maximum
throughput with a serial data stream.
--
Stan
--
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
--
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
